He came second, serving a term as deputy mayor before pursuing his musical career. He recently signed to XL Records, home to Adele and Radiohead, where he has been working with Jamie xx.

Years and Years, meanwhile, are a three-piece electro-pop outfit, who take inspiration from '90s R&B stars like Aaliyah and TLC.

Their frontman, Olly Alexander, has a parallel career in acting - having starred as Jakob in Channel 4 teen drama Skins, as well as the films Enter the Void and The Riot Club.

Irish folk singer Soak - aka Bridie Monds-Watson - has been compared to Joni Mitchell for her eviscerating portraits of teenage life.

Guitar resurgence

The longlist will be narrowed down to five in the week of 6 January, with the winner to be named on 11 January.

All but two of the nominees are British, with R&B singer Shamir and rapper Raury representing the US.

The latter, who wrote his first song - Oh, Little Fishy - at the age of three, is one of five teenagers on the longlist, most of whom describe their music as "genreless".

"I think the internet has changed music," he declared. "People like me grow up listening to everything and the genres begin to blend and disappear."

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South London rapper Stormzy is the only unsigned artist on the list

The list also sees a low-key return for guitar-based bands, whose sole representative in 2014 was rock duo Royal Blood.

Slaves, from Kent, combine rockabilly and tight, un-scruffy grunge, and are renowned for their intense live shows. Wolf Alice, who took their name from an Angela Carter short story collection, also channel the spirit of grunge on melodic, riff-heavy songs like Moaning Lisa Smile.

"We like to keep it energetic and loud," singer Ellie Roswell told the BBC.

Several of the artists on the list have been supported early in their careers by the regional BBC Introducing radio shows - with Lapsley, Rae Morris and Sunset Sons among the beneficiaries.

And several of the nominees are classically trained, including Bay and soul singer Kwabs, who attended the Royal Academy of Music.

This year, 139 music industry experts helped select the nominees. According to the rules, the acts should not already be well-known to the UK public - through featuring in the final stages of a TV talent show, for example, or having already been a member of a successful band.

They must also not have been the lead artist on a UK top 20 single or album before 27 October 2014 - though guest vocalists are eligible.

DJ Huw Stephens will announce the top five acts, counting down to the winner, live on BBC's Radio 1 breakfast show each morning from 5 January.

"It's always an exciting time of year to take stock and look at what might be making us dance, cry and jump for joy into the year ahead," he said.

"I'm excited because there are a lot of artists I and my fellow DJs have supported on the list, and it's another great chance to share the music we love with an even bigger audience".